Page 342 - Handbook Of Multiphase Flow Assurance

Flow loop tests 341

5. Adsorbed segments orientation relative to surface was not definitive. Segments were
observed with polar groups both pointing to and away from surface. This may be
explained by the rigid backbone-side group bond unable to rotate.
6. New simulated chemicals show both strong adsorption on hydrate and significant
blocking of methane adsorption in cavities. New-2-PVP and New-2-PVCap are
potentially good inhibitors and were recommended for synthesis.
7. Length of polymer chain sufficient to distinguish between good and poor inhibitors was
found to be 8. Shorter chains do not reflect the inhibitors' performance. Length of simulation
was 100,000–150,000 cycles which is at least 10 h of run-time on the CSM fastest computers.

Conclusions about kinetic inhibition mechanism

(1) Experiments with single THF hydrate crystals indicate a change in crystal growth habit
upon addition of kinetic inhibitors to the hydrate melt. This phenomenon is explained
by adsorption of polymeric chains on {111} faces of sII hydrate.
(2) Computer simulations show that polymer chains adsorb on hydrate surface with
favorable energies.
(3) Computer simulations show that polymer chains also block guest molecules from
hydrate surface. Polymer chains adsorbed on hydrate decrease the adsorption of guest
molecules into open hydrate cavities. It is likely that methophilic part of inhibitors
accumulate hydrocarbon molecules on them producing additional deficit of guest
molecules near hydrate surface.

Recommendations
(1) Make and test the new-2-PVCap and new-2-PVP.
(2) Design chemicals with side groups having a polar hydrogen-bonding part and an apolar
methophilic part.
3
(3) Monomer size should be in the range 140–170 Å which is close to the size of PVCap
monomer. Further increasing the monomer size may decrease performance.

Flow loop tests

Flow loops are a complex yet relatively easy to construct laboratory equipment. The key
components include: a pump, tubing, and a cooling system. The following studies may be
performed with a flow loop:
• Paraffin deposition
• Hydrate formation
• Multiphase flow
Some additional considerations need to be made for each of the equipment types.
• Paraffin deposition
Paraffin deposition loop requires a heated tank to dissolve any formed wax solids
before oil is recirculated into the loop. The tank volume should be at least 10 times and
preferably 100 times as large as the volume of the loop piping. Oil in the tank should be
heated to just above the wax appearance temperature.